The 3GPP LTE (Long Term Evolution) standard is the last stage in the realization of true 4th generation (4G) of mobile telephone networks. Most major mobile carriers in the United States and several worldwide carriers have announced plans to convert their networks to LTE beginning in 2009. LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS). Much of 3GPP Release 8 will focus on adopting 4G mobile communications technology, including an all-IP flat networking architecture.
The 3GPP LTE standard uses oorthogonal frequency division multiplexing (OFDM) for the downlink (i.e., from the base station to the mobile station). Orthogonal frequency division multiplexing (OFDM) is a multi-carrier transmission technique that transmits on many orthogonal frequencies (or subcarriers). The orthogonal subcarriers are individually modulated and separated in frequency such that they do not interfere with one another. This provides high spectral efficiency and resistance to multipath effects.
The following prior art reference documents are hereby incorporated into the present disclosure as if fully set forth herein:
1) 3GPP TS 36.211, v. 8.8.0 (2009-09), “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Channels And Modulation (Release 8)”, 2009 (hereafter “REF1”);
2) 3GPP TS 36.212, v. 8.8.0 (2009-12), “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing And Channel Coding (Release 8)”, 2009 (hereafter “REF2”);
3) 3GPP TS 36.213, v. 8.8.0 (2009-09), “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer Procedures (Release 8)”, 2009 (hereafter “REF3”); and
4) 3GPP TSG-RAN WG1 Meeting #59, Document No. R1-095130, “CR 36.213 Introduction Of Enhanced Dual Layer Transmission”, November 2009 (hereafter “REF4”).
For the sake of convenience, the terms “eNodeB” and “base station” may be used interchangeably herein to refer to the network infrastructure components that provide wireless access to remote terminals. However, it will be recognized by those skilled in the art that, depending on the network type, other well-known terms, such as “access point”, may be used instead of base station (BS) or eNodeB.
Also, for the sake of convenience, the terms “user equipment” and “mobile station” may be used interchangeably herein to designate any remote wireless equipment that wirelessly accesses a base station (or eNodeB), whether or not the mobile station is a truly mobile device (e.g., cell phone) or is normally considered a stationary device (e.g., desktop personal computer, vending machine, etc.). However, it will again be recognized by those skilled in the art that, depending on the network type, other well-known terms, such as “subscriber station”, “remote terminal”, or “wireless terminal”, may be used instead of user equipment (UE) or mobile station (MS).
In REF4 above, channel quality indicator (CQI) and precoding matrix indicator (PMI) are defined. The CQI indices and their interpretations are given in Table 7.2.3-1 of REF4 and are reproduced FIG. 3B. More generally, a mobile station (or user equipment) may report back to a wireless network at least one of CQI, PMI, modulation scheme, and transport block size.
Based on an unrestricted observation interval in time and frequency, the user equipment (or mobile station) derives for each CQI value reported in uplink subframe n the highest CQI index between 1 and 15 in Table 7.2.3-1 that satisfies the following condition (or CQI index 0 if CQI index 1 does not satisfy the condition): a single PDSCH transport block with a combination of modulation scheme and transport block size corresponding to the CQI index, and occupying a group of downlink physical resource blocks termed the CQI reference resource, could be received with a transport block error probability not exceeding 0.1.
A combination of modulation scheme and transport block size corresponds to a CQI index if all of the following three conditions are met: i) the combination could be signaled for transmission on the PDSCH in the CQI reference resource according to the relevant Transport Block Size table, ii) the modulation scheme is indicated by the CQI index, and iii) the combination of transport block size and modulation scheme, when applied to the reference resource, results in the code rate which is the closest possible to the code rate indicated by the CQI index. If more than one combination of transport block size and modulation scheme results in a code rate equally close to the code rate indicated by the CQI index, only the combination with the smallest of such transport block sizes is relevant.
In the CQI reference resource, the UE (or MS) shall assume the following for the purpose of deriving the CQI index: 1) the first 3 OFDM symbols are occupied by control signaling; 2) no resource elements are used by primary or secondary synchronization signals or physical broadcast channel (PBCH); 3) cyclic prefix (CP) length is that same as for the non-MBSFN subframes; 4) redundancy version 0; and 5) the physical downlink shared channel (PDSCH) transmission scheme given by Table 7.2.3-0 (reproduced herein), depending on the transmission mode currently configured for the UE or MS (which may be the default mode).
For the purpose of deriving the CQI index, the UE (or MS) also shall assume that the ratio of PDSCH energy per resource element (EPRE) to cell-specific reference signal (RS) EPRE is as given in Section 5.2 (Downlink Power Allocation) of REF3 above, with the exception of the ρA value, which shall be assumed to be:ρA=PA+Δoffset+10 log10(2) (dB)  [Eqn. 1]for any modulation scheme, if the UE (or MS) is configured with transmission mode 2 with 4 cell-specific antenna ports, or transmission mode 3 with 4 cell-specific antenna ports and the associated rank indicator (RI) is equal to one; orρA=PA+Δoffset (dB)  [Eqn. 2]for any modulation scheme and any number of layers, otherwise.
The shift Δoffset is given by the parameter nomPDSCH-RS-EPRE-Offset which is configured by higher-layer signaling.
Precoding Matrix Indicator (PMI)
For transmission modes 4, 5 and 6 in Table 7.2.3-0, precoding feedback is used for channel dependent codebook-based precoding and relies on each UE reporting the precoding matrix indicator (PMI) value. For transmission mode 8, the UE/MS shall report the PMI value if the US/MS is configured with PMI/RI reporting. A UE shall report PMI based on the feedback modes described in Sections 7.2.1 and 7.2.2 of REF3.
Each PMI value corresponds to a codebook index given in Table 6.3.4.2.3-1 or Table 6.3.4.2.3-2 of REF3 as follows: 1) for 2 antenna ports {0,1} and an associated rank indication (RI) value of 1, a PMI value of nε{0,1,2,3} corresponds to the codebook index n given in Table 6.3.4.2.3-1 of REF3 with υ=1; 2) for 2 antenna ports {0,1} and an associated RI value of 2, a PMI value of n E {0,1} corresponds to the codebook index n+1 given in Table 6.3.4.2.3-1 of REF3 with υ=2; and 3) for 4 antenna ports {0,1,2,3}, a PMI value of nε{0,1,2, . . . ,15} corresponds to the codebook index n given in Table 6.3.4.2.3-2 of REF3 with U equal to the associated RI value. For other transmission modes, PMI reporting is not supported.
In Section 5 (Power Control) of REF3, it is noted that downlink power control determines the energy per resource element (EPRE). The term “resource element energy” denotes the energy prior to CP insertion. The term “resource element energy” also denotes the average energy taken over all constellation points for the modulation scheme applied. Uplink power control determines the average power over a single carrier, frequency division multiple access (SC-FDMA) symbol in which the physical channel is transmitted.
In Section 5.2 (Downlink Power Allocation) of REF3, it is noted that eNodeB (or the base station) determines the downlink transmit energy per resource element. The user equipment (UE) or mobile station (MS) may assume downlink cell-specific, reference signal energy per resource element (RS EPRE) is constant across the downlink system bandwidth and constant across all subframes until different cell-specific RS power information is received.
FIG. 4 illustrates a resource block (RB) in a 3GPP LTE system according to an exemplary embodiment of the prior art. In Release 8 of 3GPP, downlink (DL) power allocation indicates to a UE (or MS) an EPRE map that may be assumed for the purpose of demodulation for each cell-specific antenna port (or cell-specific reference signal (RS) port or CRS port). FIG. 4 illustrates an exemplary EPRE map for a resource block (RB) in Release 8.
The resource block in FIG. 4 depicts part of a physical downlink shared channel (PDSCH) of a subframe. The horizontal axis indicates time. The vertical axis indicates frequency. In FIG. 4, each OFDM symbol is aligned vertically. The squares in each vertical column represent different subcarrier frequencies that are part of the same OFDM symbol. The squares in each horizontal row represent the same subcarrier frequency in different OFDM symbols. Thus, each square represents a time-frequency resource element (RE) that may be individually modulated to transmit information.
Each OFDM symbol comprises N sequential subcarriers, where N may be, for example, 512, 1024, 2048, and so forth. As noted, each subcarrier may be individually modulated. For practical reasons, only a small segment of each OFDM symbol may be shown for the resource block (RB) in FIG. 4. The exemplary RB spans an exemplary one (1) millisecond subframe, where each subframe comprises two (2) slots, each equal to 0.5 milliseconds in duration. The subframe contains 14 sequential OFDM symbols, so that each slot contains 7 sequential OFDM symbols. The 7 OFDM symbols in each slot are labeled S0, S1, S2, S3, S4, S5, and S6. However, this is by way of example only and should not be construed to limit the scope of the present disclosure. In alternate embodiments, the slots may be greater than or less than 0.5 milliseconds in duration and a subframe may contain more than or less than 14 OFDM symbols.
In the exemplary embodiment, the resource block (RB) spans 12 sequential subcarriers in the frequency dimension and 14 OFDM symbols in the time dimension. Thus, the RB contains 168 time-frequency resources. Again, however, this is by of example only. In alternate embodiments, the RB may span more than or less than 12 subcarriers and more than or less than 14 OFDM symbols, so that the total number of resource elements (REs) in the RB may vary. In a multi-antenna system, such as a multiple-input, multiple-output (MIMO) base station, the subcarriers labeled CRS P0, CRS P1, CRS P2, and CRS P3 represent cell-specific reference signals (e.g., pilot signals) for a particular antenna port. Thus, for example, CRS PO is the cell-specific reference signal (CRS) for antenna port 0. For the purposes of this disclosure, it shall be assumed that the EPRE for each of CRS P0, CRS P1, CRS P2, and CRS P3 (i.e., the antenna ports) is the value, P.
The data EPRE values in FIG. 4 are denoted by letters A and B, depending on type of OFDM symbols on which data EPREs are located. When a data resource element (RE) is located in an OFDM symbol that does not contain a CRS resource element (RE), the EPRE is denoted by the value, A. By way of example, OFDM symbol S3 in the even-numbered slot in FIG. 4 does not contain a CRS RE, therefore each data RE in OFDM symbol S3 is labeled A. When a data RE is located in an OFDM symbol that does contain a CRS RE, the EPRE is denoted by the value, B. By way of example, OFDM symbol S4 in the even-numbered slot in FIG. 4 does contain CRS REs, therefore each data RE in OFDM symbol S4 is labeled B.
A Release 8 base station (or eNodeB) signals three parameters to a UE (or MS) to indicate to the UE the EPRE map associated with the UE, including two cell-specific parameters and one UE-specific parameter. The two cell-specific parameters are the CRS value, P, and ρB/ρA=B/A, where ρA=A/P and ρB=B/P. The one UE-specific parameter is the power ratio of A to P, or ρA=A/P. Using these three parameters from the eNodeB, a UE is capable of determining the EPRE map in FIG. 4.
DM-RS Patterns
The demodulation reference signal (DM-RS) may also be called the dedicated RS (DRS) or UE-specific RS (UE-RS). The DRS is transmitted by the base station (or eNodeB) and is used for demodulation by the UE. A DRS for a data stream (or layer) is precoded with the same precoding vector that is used for precoding the data stream.
FIGS. 5A-5C illustrate 2 DRS patterns and 4 DRS patterns in resource blocks according to exemplary embodiments of the prior art. Resource block (RB) 500A in FIG. 5A depicts Rank-2 DRS Pattern A for a pilot signal pattern that can support up to 2 layer transmissions. Resource block (RB) 500B in FIG. 5B depicts Rank-2 DRS Pattern B for a pilot signal pattern that can support up to 2 layer transmissions. The reference signals for the two layers are code-division multiplexed within a pair of two adjacent DRS resource elements. Thus, in FIG. 5A, each instance of two adjacent resource elements labeled DRS P7,8 indicates code-division multiplexed DRS REs for antenna port 7 and antenna port 8. Similarly, in FIG. 5B, each instance of two adjacent resource elements labeled DRS P9,10 indicates code-division multiplexed DRS REs for antenna port 9 and antenna port 10.
Resource block 500C in FIG. 5C depicts a DRS pattern that supports up to four layer transmissions, where DRS resource elements are partitioned into two groups. One group of DRS REs carries the code-division multiplexed dedicated reference signals (DRSs) for antenna ports 7 and 8 (for layers 0 and 1). The other group of DRS REs carries the code-division multiplexed dedicated reference signals (DRSs) for antenna ports 9 and 10 (for layers 2 and 3).
FIGS. 6A and 6B illustrate 8 DRS patterns based on DRS code-division multiplexing in resource blocks according to exemplary embodiments of the prior art. In FIGS. 6A and 6B, some resource element (RE) are labeled with one of the alphabet characters G, H, I, J, L, or K, to indicate the RE is used to carry a number of DRS among the 8 DRS.
Resource block (RB) 600A in FIG. 6A depicts Rank-8 pattern A, which is based on spreading factor 2 code-division multiplexing (CDM) across two time-adjacent REs with the same alphabet label. Resource block (RB) 600B in FIG. 6B depicts Rank-8 pattern B, which is based on spreading factor 4 code-division multiplexing across two groups of two time-adjacent REs with the same alphabet label.
The 8 antenna ports in the Rank-8 patterns in FIGS. 6A and 6B are referred to as antenna ports 11 through 18 to distinguish the Rank-8 patterns from the antenna ports in the Rank-2 and Rank-4 pattern. Thus, for the Rank-8 Pattern A in FIG. 6A, the two adjacent resource elements labeled DRS G carry the CDMed DRS 11, 12. The two adjacent resource elements labeled DRS H carry the CDMed DRS 13, 14. The two adjacent resource elements labeled DRS I carry the CDMed DRS 15, 16. The two adjacent resource elements labeled DRS J carry the CDMed DRS 17, 18.
On the other hand, for the Rank-8 Pattern B in FIG. 6B, the two adjacent resource elements labeled DRS K carry the CDMed DRS 11, 12, 13, 14. Similarly, the two adjacent resource elements labeled DRS L carry the CDMed DRS 15, 16, 17, 18.
Control Signaling
Generally, there are two types of signaling: higher-layer signaling and physical-layer signaling. Higher-layer signaling includes broadcast signaling and RRC signaling, which can be semi-static signaling. Broadcast signaling lets the UEs know cell-specific information, while RRC signaling lets the UEs know UE-specific information.
Physical-layer signaling includes dynamic signaling, where the dynamic signaling may happen in a physical downlink control channel (PDCCH) in those subframes where the BS or eNodeB wants to transmit signals to the Ms (or UE). For this type of dynamic signaling, a downlink control information (DCI) format may be defined, where DCI is transmitted in the PDCCH.
U.S. patent application Ser. No. 12/899,362, entitled “Methods And Apparatus For Multi-User MIMO Transmission in Wireless Communication Systems” and filed Oct. 6, 2010, introduced DCI format 2C for LTE Release 10 downlink (DL) grant supporting up to rank 8. The DCI format 2C is based on DCI format 2B. U.S. patent application Ser. No. 12/899,362 is hereby incorporated into the present application as if fully set forth herein.
A transport block (TB) is a bit stream carried from a higher layer. In the physical layer, a TB is mapped into a codeword (CW). In Release 8 LTE, up to two TBs (and thus up to two CWs) can be scheduled to a UE in a set of time-frequency resources in a subframe.
CSI-RS Transmissions
U.S. patent application Ser. No. 12/709,399, entitled “Method And System For Mapping Pilot signals In Multi-Stream Transmissions” and filed Feb. 19, 2010, introduced mapping methods for channel-state-information (CSI) reference signals, sometimes called channel-quality-information RS (or CSI-RS). U.S. patent application Ser. No. 12/709,399 is hereby incorporated into the present application as if fully set forth herein.
A channel-state-information reference signal (CSI-RS) mapping pattern is defined as a set of resource elements (REs) in one resource block (RB) spanning two slots (or one subframe), where the pattern repeats in every RB in a subset or in the set of RBs in the system bandwidth. CSI-RS resource elements may reside in only one slot or in both slots in a RB in one subframe. A CSI-RS mapping pattern is provided for estimating channel state information at the receiver side for multiple transmit (Tx) antenna port channels. CSI may include channel quality information (CQI), rank information (RI), precoding matrix information (PMI), channel direction information (CDI), and so forth.
However, CSI subframes (i.e., subframes where CSI-RSs are transmitted) may be transmitted periodically (e.g., every 5 subframes) or aperiodically. FIG. 7 illustrates an example of CSI-RS mapping in subframes in a radio frame. In FIG. 7, there are four types of subframes, depending on whether or not CSI-RS resources elements and CRS resource elements are allocated in the PDSCH region. For example, a Type A subframe (SF) does not contain CSI-RS, but does contain CRS in the PDSCH region. Subframe 0 (SF0), Subframe 1 (SF1), Subframe 3 (SF3), Subframe 5 (SF5), Subframe 8 (SF8) and Subframe 9 (SF9) are Type A subframes.
The user equipment uses the CSI-RS resource elements and the CRS resource elements (among others) to determine and to report back to a wireless network at least one of CQI, PMI, modulation scheme, and transport block (TB) size. It is noted that in a given network, not all four types of subframe may be present. Therefore, CSI-RS and CRS resource elements may not be present in certain subframe (SF) types. Thus, interpretation of the feedback data (i.e., CQI, PMI, modulation scheme, TB size) is dependent on the type of subframe the MS/UE receives.
However, the prior art does not provide a mobile station (or UE) that considers the subframe (SF) type when determining CQI, PMI, and other feedback parameters. The prior art also does not provide a base station that interprets feedback parameters based on the SF type assumed by the MS/UE when determining the feedback parameters. Thus, there is a need in the art for improved apparatuses and methods that account for SF type in the determination and interpretation of feedback parameters.